Anchoring systems with expansion elements and sleeve elements made of a plastics material and corresponding methods for anchoring in an anchoring base, such as concrete or masonry for example, are known in the state of the art.
In order to make an anchor with an anchoring system of this kind, the sleeve element, such as a dowel, is first inserted into a drill hole in the anchoring base. After that, the expansion element, such as a steel screw, with a threaded portion is screwed into the sleeve element. The expansion element usually has an external diameter, such as a core diameter, which is at least in some sections larger than the internal diameter of the sleeve element. Because of this overwidth, as the screw is screwed in, the plastics material of the sleeve element is displaced radially outwards, so that an expansion pressure is created, with which the sleeve element is pressed against the wall of the drill hole.
The extraction resistance which has to be overcome in order to pull the sleeve element out of the drill hole is determined principally by the expansion pressure and the coefficient of friction between the sleeve element and the wall of the drill hole. The coefficient of friction is dependent both on the material of the anchoring base and the sleeve element, and on the surface properties or surface geometry of the wall of the drill hole and the external surface of the sleeve element.
Raising the overwidth of the expansion element diameter relative to the internal diameter of the sleeve element cannot increase the expansion pressure and hence the extraction resistance to an infinite extent, however, because the amount of heat introduced into the plastics material is intensified at the same time. The heat load can impair the properties of the plastics material, which in turn limits the increase in the extraction resistance.